Uptake Of Ketone Bodies Research Articles

Lower GLUT1 and unchanged MCT1 in Alzheimer’s disease cerebrovasculature

The brain is a highly demanding organ, utilizing mainly glucose but also ketone bodies as sources of energy. Glucose transporter-1 (GLUT1) and monocarboxylates transporter-1 (MCT1) respectively transport glucose and ketone bodies across the blood-brain barrier. While reduced glucose uptake by the brain is one of the earliest signs of Alzheimer’s disease (AD), no change in the uptake of ketone bodies has been evidenced yet. To probe for changes in GLUT1 and MCT1, we performed Western immunoblotting in microvessel extracts from the parietal cortex of 60 participants of the Religious Orders Study. Participants clinically diagnosed with AD had lower cerebrovascular levels of GLUT1, whereas MCT1 remained unchanged. GLUT1 reduction was associated with lower cognitive scores. No such association was found for MCT1. GLUT1 was inversely correlated with neuritic plaques and cerebrovascular β-secretase-derived fragment levels. No other significant associations were found between both transporters, markers of Aβ and tau pathologies, sex, age at death or apolipoprotein-ε4 genotype. These results suggest that, while a deficit of GLUT1 may underlie the reduced transport of glucose to the brain in AD, no such impairment occurs for MCT1. This study thus supports the exploration of ketone bodies as an alternative energy source for the aging brain.

ICS II protects against cardiac hypertrophy by regulating metabolic remodelling, not by inhibiting autophagy

Cardiac hypertrophy is characterized by a shift in metabolic substrate utilization. Therefore, the regulation of ketone body uptake and metabolism may have beneficial effects on heart injuries that induce cardiac remodelling. In this study, we investigated whether icariside II (ICS II) protects against cardiac hypertrophy in mice and cardiomyocytes. To create cardiac hypertrophy animal and cell models, mice were subjected to transverse aortic constriction (TAC), and embryonic rat cardiomyocytes (H9C2) were stimulated with angiotensin II, a neurohumoral stressor. Both the in vivo and in vitro results suggest that ICS II treatment ameliorated pressure overload–induced cardiac hypertrophy and preserved heart function. In addition, apoptosis and oxidative stress were reduced in the presence of ICS II. Moreover, ICS II inhibited excess autophagy in TAC‐induced hearts and angiotensin II–stimulated cardiomyocytes. Mechanistically, we found that ICS II administration regulated SIRT3 expression in cardiac remodelling. SIRT3 activation increased ketone body transportation and utilization. Collectively, our data show that ICS II attenuated cardiac hypertrophy by modulating ketone body and fatty acid metabolism, and that this was likely due to the activation of the SIRT3‐AMPK pathway. ICS II treatment may provide a new therapeutic strategy for improving myocardial metabolism in cardiac hypertrophy and heart failure.

A 48‐year‐old female, with a family history of AD PSEN1 mutation, who developed mild cognitive impairment and tried ketogenic diet‐associated medium‐chain triglyceride as treatment

AbstractBackground48 years old female, biologist researchers, with a family history of AD PSEN1 mutation, symptoms compatible with Mild Cognitive Impairment (MCI) due to probable Alzheimer's disease. As part of clinical approach Ketogenic Diet and medium‐chain triglyceride was tried combined with conventional treatment.Methodthe patient had a 2 ‐year long history of amnestic symptoms with a slow worsening, when medical help was sought. She underwent neurological and neuropsychological evaluation, magnetic resonance and specific genetic tests. It was observed memory and attention deficit, executive functions impairment; left hippocampal atrophy, ApoE E2/E3 profile and a variant of uncertain significance of PSEN1. At 48, she was classified as Mild Cognitive Impairment and started a treatment with middle‐chain triglycerides and Ketogenic Diet. Before starting the treatment, she underwent another neuropsychological evaluation, PET‐FDG and cerebrospinal fluid biomarkers profile. During the treatment, she will be monitored weekly by a nutritionist expert in ketogenic diet. After three months of treatment, she will repeat tests and exams.ResultCurrently, the patient is being treated, until March 2020, at the end of it she will repeat tests and exams. According to previous studies1, 6 weeks of modified ketogenic diet, is associated with an improvement of the cerebrospinal fluid biomarker profile, cerebral perfusion, and cerebral ketone body uptake, in older adult with risk for Alzheimer Disease.ConclusionThis case is of great importance in describing a woman’s history with the PSEN1 mutation, who underwent a Ketogenic Diet treatment while diagnosed with MCI. Regardless of the outcome, this case is essential to identify the effects of ketogenic diets on the biomarkers and neuropsychological tests on patients with the same profile.

Modified ketogenic diet is associated with improved cerebrospinal fluid biomarker profile, cerebral perfusion, and cerebral ketone body uptake in older adults at risk for Alzheimer’s disease: a pilot study

There is currently no established therapy to treat or prevent Alzheimer’s disease. The ketogenic diet supplies an alternative cerebral metabolic fuel, with potential neuroprotective effects. Our goal was to compare the effects of a modified Mediterranean-ketogenic diet (MMKD) and an American Heart Association Diet (AHAD) on cerebrospinal fluid Alzheimer’s biomarkers, neuroimaging measures, peripheral metabolism, and cognition in older adults at risk for Alzheimer’s. Twenty participants with subjective memory complaints (n = 11) or mild cognitive impairment (n = 9) completed both diets, with 3 participants discontinuing early. Mean compliance rates were 90% for MMKD and 95% for AHAD. All participants had improved metabolic indices following MMKD. MMKD was associated with increased cerebrospinal fluid Aβ42 and decreased tau. There was increased cerebral perfusion and increased cerebral ketone body uptake (11C-acetoacetate PET, in subsample) following MMKD. Memory performance improved after both diets, which may be due to practice effects. Our results suggest that a ketogenic intervention targeted toward adults at risk for Alzheimer’s may prove beneficial in the prevention of cognitive decline.

Effect of Annona muricata Leaves Extract on Colon Antioxidant Status and Ketone Bodies in Blood and Urine of Cycas-treated Rats

The effect of Annona muricata methanol leaf extract (AMELE) on colon antioxidant status and ketone bodies in blood and urine of cycas treated rats was investigated. Seventy male Wistar albino rats were randomly assigned into seven groups of ten experimental animals in a study that lasted for twenty-eight days. After 28 days, using standard methods, serum and urinary ketone bodies were assayed. Malondialdehyde (MDA), antioxidants enzymes in the colon and histopathological analysis were assayed. The results showed ketogenic diet had significant (p<0.05) increase in serum and urinary ketone body levels compared to other groups on normal feed. Annona muricata extract enhanced cellular consumption and uptake of ketone bodies whereas cycas reduced cellular consumption of ketone bodies. Annona muricata given either with ketogenic diet or cycas or with both ketogenic diet and cycas led to higher tissue levels of antioxidant enzymes. Tissue MDA levels were significantly (p<0.05) increased in all cycas treated groups compared to the control group with the highest levels seen in the two groups placed on normal feed and cycas. Lactate dehydrogenase activities were significantly (p<0.05) increases in all the groups placed on ketogenic diet compared to the groups placed on normal feed. Histopathological analysis revealed normal rat colon tissues in all the groups except 43% of the group 2 animals. This therefore indicates that cycas- induced oxidative stress and tissue injury may be mitigated by the combined administration of Annona muricata extract and ketogenic diet.

Correction to: Increased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular Remodeling.

HomeCirculation: Heart FailureVol. 12, No. 3Correction to: Increased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular Remodeling Free AccessCorrectionPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessCorrectionPDF/EPUBCorrection to: Increased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular Remodeling Originally published25 Feb 2019https://doi.org/10.1161/HHF.0000000000000035Circulation: Heart Failure. 2019;12:e000035This article corrects the followingIncreased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular RemodelingIn the article by Voros et al, “Increased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular Remodeling,” which appeared in the December 2018 issue of the journal (Circ Heart Fail.2018;11:e004953), a correction was needed.Authors Pieter Vermeersch and Stefan Janssens should be designated as having contributed equally to the work as co-senior authors.The authors regret this error.These corrections have been made to the current version of the article, which is available at https://www.ahajournals.org/doi/10.1161/CIRCHEARTFAILURE.118.004953. Previous Back to top Next FiguresReferencesRelatedDetailsRelated articlesIncreased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular RemodelingGabor Voros, et al. Circulation: Heart Failure. 2018;11 March 2019Vol 12, Issue 3 Advertisement Article InformationMetrics © 2019 American Heart Association, Inc.https://doi.org/10.1161/HHF.0000000000000035PMID: 30888850 Originally publishedFebruary 25, 2019 PDF download Advertisement

Increased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular Remodeling.

Deranged energy metabolism contributes to the pathophysiology of heart failure (HF). Recent studies showed diminished free fatty acid (FFA) oxidation in experimental HF models with a shift towards oxidation of ketone bodies. However, conflicting clinical data on FFA metabolism and limited knowledge on ketone body metabolism in human HF mandate additional metabolic profiling studies. We, therefore, investigated cardiac uptake of FFAs and ketone bodies (β-hydroxybutyrate and acetoacetate) in patients with HF with reduced ejection fraction (HFrEF) or with aortic stenosis (AS)-induced left ventricular hypertrophy. We hypothesized that FFA oxidation is impaired in HFrEF and in AS and results in decreased concentrations of free carnitine, the necessary carrier for mitochondrial entry of activated FFAs, and in accumulation of metabolic intermediates. We collected arterial and coronary sinus blood samples in patients with HFrEF (n=15), in AS patients with preserved systolic function (n=15), and in control patients (n=15). Plasma concentration gradients across the heart show significantly greater uptake of ketone bodies in patients with HFrEF than in controls. Patients with AS show significantly increased uptake of β-hydroxybutyrate and FFAs. Free carnitine concentration and concentration gradients of intermediates of FFA oxidation were comparable between groups. In conclusion, our results show significantly increased cardiac uptake of ketone bodies in patients with stable HFrEF and AS and increased uptake of FFAs in AS compared with control patients. The lack of myocardial release of acyl-carnitine species or change in free carnitine uptake suggests no impairment of FFA oxidation.

Human ApoE Isoforms Differentially Modulate Brain Glucose and Ketone Body Metabolism: Implications for Alzheimer's Disease Risk Reduction and Early Intervention.

Humans possess three genetic isoforms of apolipoprotein E (ApoE)-ApoE2, ApoE3, and ApoE4-that confer differential risk for Alzheimer's disease (AD); however, the underlying mechanisms are poorly understood. This study sought to investigate the impact of human ApoE isoforms on brain energy metabolism, an area significantly perturbed in preclinical AD. A TaqMan custom array was performed to examine the expression of a total of 43 genes involved in glucose and ketone body transport and metabolism, focusing on pathways leading to the generation of acetyl-CoA, in human ApoE gene-targeted replacement female mice. Consistent with our previous findings, brains expressing ApoE2 exhibited the most robust profile, whereas brains expressing ApoE4 displayed the most deficient profile on the uptake and metabolism of glucose, the primary fuel for the brain. Specifically, the three ApoE brains differed significantly in facilitated glucose transporters, which mediate the entry of glucose into neurons, and hexokinases, which act as the "gateway enzyme" in glucose metabolism. Interestingly, on the uptake and metabolism of ketone bodies, the secondary energy source for the brain, ApoE2 and ApoE4 brains showed a similar level of robustness, whereas ApoE3 brains presented a relatively deficient profile. Further, ingenuity pathway analysis indicated that the PPAR-γ/PGC-1α signaling pathway could be activated in the ApoE2 brain and inhibited in the ApoE4 brain. Notably, PGC-1α overexpression ameliorated ApoE4-induced deficits in glycolysis and mitochondrial respiration. Overall, our data provide additional evidence that human ApoE isoforms differentially modulate brain bioenergetic metabolism, which could serve as a potential mechanism contributing to their discrete risk impact in AD.SIGNIFICANCE STATEMENT We uncovered hexokinase as a key cytosolic point in the glucose metabolism that is differentially modulated by the three ApoE genotypes. The differences in hexokinase expression and activity exhibited in the three ApoE brains may underlie their distinct impact on brain glucose utilization and further susceptibility to AD. Therefore, a therapeutic approach that could circumvent the deficiencies in the cytosolic metabolism of glucose by providing glucose metabolizing intermediates, e.g., pyruvate, may hold benefits for ApoE4 carriers, who are at high risk for AD. The bioenergetic robustness may translate into enhanced synaptic activity and, ultimately, reduces the risk of developing AD and/or delays the onset of clinical manifestation.

Acute and Chronic Increases of Circulating FSTL1 Normalize Energy Substrate Metabolism in Pacing-Induced Heart Failure.

FSTL1 (follistatin-like protein 1) is an emerging cardiokine/myokine that is upregulated in heart failure (HF) and is found to be cardioprotective in animal models of cardiac injury. We tested the hypothesis that circulating FSTL1 can affect cardiac function and metabolism under baseline physiological conditions and in HF. FSTL1 was acutely (10 minutes) or chronically (2 weeks) infused to attain clinically relevant blood levels in conscious dogs with cardiac tachypacing-induced HF. Dogs with no cardiac pacing and FSTL1 infusion served as control. 3H-oleate and 14C-glucose were infused to track the metabolic fate of free fatty acids and glucose. Cardiac uptake of lactate and ketone bodies and systemic respiratory quotient were also measured. HF caused a shift from prevalent cardiac and systemic fat to carbohydrate oxidation. Although acute FSTL1 administration caused minimal hemodynamic changes at baseline, in HF dogs it enhanced cardiac oxygen consumption and transiently reversed the changes in free fatty acid and glucose oxidation and systemic respiratory quotient. In HF, chronic FSTL1 infusion stably normalized cardiac free fatty acid, glucose, ketone body consumption, and systemic respiratory quotient, while moderately improving diastolic and contractile function. Consistently, FSTL1 prevented the downregulation of medium-chain acyl-CoA dehydrogenase-a representative enzyme of the free fatty acid oxidation pathway. Complementary in vitro experiments in primary cardiac and skeletal muscle myocytes showed that FSTL1 stimulated oxygen consumption through AMPK (AMP-activated kinase) activation. These findings support a novel function for FSTL1 and provide the first direct evidence that a circulating cardiokine/myokine can alter myocardial and systemic energy substrate metabolism, in vivo.

Targeting Tumor Mitochondrial Metabolism Overcomes Resistance to Antiangiogenics.

Epithelial malignancies are effectively treated by antiangiogenics; however, acquired resistance is a major problem in cancer therapeutics. Epithelial tumors commonly have mutations in the MAPK/Pi3K-AKT pathways, which leads to high-rate aerobic glycolysis. Here, we show how multikinase inhibitor antiangiogenics (TKIs) induce hypoxia correction in spontaneous breast and lung tumor models. When this happens, the tumors downregulate glycolysis and switch to long-term reliance on mitochondrial respiration. A transcriptomic, metabolomic, and phosphoproteomic study revealed that this metabolic switch is mediated by downregulation of HIF1α and AKT and upregulation of AMPK, allowing uptake and degradation of fatty acids and ketone bodies. The switch renders mitochondrial respiration necessary for tumor survival. Agents like phenformin or ME344 induce synergistic tumor control when combined with TKIs, leading to metabolic synthetic lethality. Our study uncovers mechanistic insights in the process of tumor resistance to TKIs and may have clinical applicability.

Altered expression of brain monocarboxylate transporter 1 in models of temporal lobe epilepsy

Monocarboxylate transporter 1 (MCT1) facilitates the transport of monocarboxylate fuels (lactate, pyruvate and ketone bodies) and acidic drugs, such as valproic acid, across cell membranes. We recently reported that MCT1 is deficient on microvessels in the epileptogenic hippocampal formation in patients with medication-refractory temporal lobe epilepsy (TLE). To further define the role of MCT1 in the pathophysiology of TLE, we used immunohistochemistry and stereological analysis to localize and quantify the transporter in the hippocampal formation in three novel and highly relevant rat models of TLE and in nonepileptic control animals. One model utilizes methionine sulfoximine to induce brain glutamine synthetase deficiency and recurrent limbic seizures, while two models employ an episode of perforant pathway stimulation to cause epilepsy. MCT1 was lost on microvessels and upregulated on astrocytes in the hippocampal formation in all models of TLE. Notably, the loss of MCT1 on microvessels was not due to a reduction in microvessel density. The similarities in MCT1 expression among human subjects with TLE and several animal models of the disease strongly suggest a critical role of this molecule in the pathogenesis of TLE. We hypothesize that the downregulation of MCT1 may promote seizures via impaired uptake of ketone bodies and antiepileptic drugs by the epileptogenic brain. We also propose that the overexpression of MCT1 on astrocytes may lead to increased uptake or release of monocarboxylates by these cells, with important implications for brain metabolism and excitability. These hypotheses can now be rigorously tested in several animal models that replicate key features of human TLE.

Food Deprivation Induces Monocarboxylate Transporter 2 Expression in the Brainstem of Female Rat

Ketone bodies are considered to act as a signal to suppress gonadotropin release during negative energy balance. The present study examined the effect of 48-h fasting on the mRNA expressions of monocarboxylate transporter 1 (MCT1) and MCT2, which are involved in ketone body transport, in several brain regions. Quantitative real-time RT-PCR analysis showed that the MCT2 mRNA levels were significantly increased by 48-h fasting in the area postrema-solitary tract nucleus (AP-NTS) region but not the arcuate nucleus-ventromedial hypothalamic nucleus (ARC-VMH) and central gray-supragenual nucleus around the 4th ventricle (CG-SGe) regions. Fasting did not significantly affect MCT1 mRNA expression in any of the brain areas examined. Luteinizing hormone (LH) pulse frequency significantly decreased and plasma concentrations of beta-hydroxybutyric acid, a ketone body, significantly increased after 48-h fasting. The present results suggest that increased uptake of ketone bodies via MCT2 in the AP-NTS region is likely involved in the mechanism of fasting-induced suppression of LH secretion in rats.

Sodium-coupled Monocarboxylate Transporters in Normal Tissues and in Cancer

SLC5A8 and SLC5A12 are sodium-coupled monocarboxylate transporters (SMCTs), the former being a high-affinity type and the latter a low-affinity type. Both transport a variety of monocarboxylates in a Na(+)-coupled manner. They are expressed in the gastrointestinal tract, kidney, thyroid, brain, and retina. SLC5A8 is localized to the apical membrane of epithelial cells lining the intestinal tract and proximal tubule. In the brain and retina, its expression is restricted to neurons and the retinal pigment epithelium. The physiologic functions of SLC5A8 include absorption of short-chain fatty acids in the colon and small intestine, reabsorption of lactate and pyruvate in the kidney, and cellular uptake of lactate and ketone bodies in neurons. It also transports the B-complex vitamin nicotinate. SLC5A12 is also localized to the apical membrane of epithelial cells lining the intestinal tract and proximal tubule. In the brain and retina, its expression is restricted to astrocytes and Müller cells. SLC5A8 also functions as a tumor suppressor; its expression is silenced in tumors of colon, thyroid, stomach, kidney, and brain. The tumor-suppressive function is related to its ability to mediate concentrative uptake of butyrate, propionate, and pyruvate, all of which are inhibitors of histone deacetylases. SLC5A8 can also transport a variety of pharmacologically relevant monocarboxylates, including salicylates, benzoate, and gamma-hydroxybutyrate. Non-steroidal anti-inflammatory drugs such as ibuprofen, ketoprofen, and fenoprofen, also interact with SLC5A8. These drugs are not transportable substrates for SLC5A8, but instead function as blockers of the transporter. Relatively less is known on the role of SLC5A12 in drug transport.

Ketone bodies metabolism during ischemic and reperfusion brain injuries following bilateral occlusion of common carotid arteries in rats

To evaluate the in vivo alterations on ketone bodies metabolism after cerebral ischemia/reperfusion through an experimental model of brain ischemia induced by simple occlusion of common carotid arteries (CCAs) in Wistar rats. Forty-eight male Wistar rats were randomly distributed on two groups (S - Sham; T - Test) and further redistributed into four times sets of study. After bilateral occlusion of CCAs for 30 min, the animals of group T were allowed reperfusion for 0, 5, 10 and 15 min. Samples of cerebral tissue and systemic arterial blood were collected and the metabolites acetoacetate (ACT) and beta-hydroxybutyrate (BHB) were determined. Cerebral ACT and BHB levels increased significantly in Group T after 30 min of carotid occlusion (time 0). The highest brain ketone bodies (ACT+BHB) concentration was verified at 5 min of reperfusion, decreasing after 10 min of recirculation. Systemic ketone bodies levels increased similarly between test and sham groups. Group S demonstrated a significant increase in cerebral and systemic ACT and BHB concentrations mainly after 40-45 min of study. The partial transient acute global brain ischemia induced by the bilateral carotid occlusion in Wistar rats triggered ketogenesis probably due to a central stimulation of catecholamine secretion. There was an increased cerebral uptake of ketone bodies following brain ischemia, reaffirming these metabolites as alternative energy substrates under conditions of cerebral metabolic stress as well as its potential role on neuroprotection. The greatest changes in ketone bodies metabolism were verified at initial minutes of recirculation as a result of the reperfusion injury phenomenon.

Isotopomer analysis of myocardial substrate metabolism: A systems biology approach

The increasing accessibility of mass isotopomer data via GC-MS and NMR technology has necessitated the use of a systematic and reliable method to take advantage of such data for flux analysis. Here we applied a nonlinear, optimization-based method to study substrate metabolism in cardiomyocytes using (13)C data from perfused mouse hearts. The myocardial metabolic network used in this study accounts for 257 reactions and 240 metabolites, which are further compartmentalized into extracellular space, cytosol, and mitochondrial matrix. Analysis of the perfused mouse heart showed that the steady-state ATP production rate was 16.6 +/- 2.3 micromol/min . gww, with 30% of the ATP coming from glycolysis. Of the four substrates available in the perfusate (glucose, pyruvate, lactate, and oleate), exogenous glucose forms the majority of cytosolic pyruvate. Pyruvate decaboxylation is significantly higher than carboxylation, suggesting that anaplerosis is low in the perfused heart. Exchange fluxes were predicted to be high for reversible enzymes in the citric acid cycle (CAC), but low in the glycolytic pathway. Pseudoketogenesis amounted to approximately 50% of the net ketone body uptake. Sensitivity analysis showed that the estimated flux distributions were relatively insensitive to experimental errors. The application of isotopomer data drastically improved the estimation of reaction fluxes compared to results computed with respect to reaction stoichiometry alone. Further study of 12 commonly used (13)C glucose mixtures showed that the mixtures of 20% [U-(13)C(6)] glucose, 80% [3 (13)C] glucose and 20% [U-(13)C(6)] glucose, 80% [4 (13)C] were best for resolving fluxes in the current network.

Candidate Metabolic Network States in Human Mitochondria: IMPACT OF DIABETES, ISCHEMIA, AND DIET

The human mitochondrial metabolic network was recently reconstructed based on proteomic and biochemical data. Linear programming and uniform random sampling were applied herein to identify candidate steady states of the metabolic network that were consistent with the imposed physico-chemical constraints and available experimental data. The activity of the mitochondrion was studied under four metabolic conditions: normal physiologic, diabetic, ischemic, and dietetic. Pairwise correlations between steady-state reaction fluxes were calculated in each condition to evaluate the dependence among the reactions in the network. Applying constraints on exchange fluxes resulted in predictions for intracellular fluxes that agreed with experimental data. Analyses of the steady-state flux distributions showed that the experimentally observed reduced activity of pyruvate dehydrogenase in vivo could be a result of stoichiometric constraints and therefore would not necessarily require enzymatic inhibition. The observed changes in the energy metabolism of the mitochondrion under diabetic conditions were used to evaluate the impact of previously suggested treatments. The results showed that neither normalized glucose uptake nor decreased ketone body uptake have a positive effect on the mitochondrial energy metabolism or network flexibility. Taken together, this study showed that sampling of the steady-state flux space is a powerful method to investigate network properties under different conditions and provides a basis for in silico evaluations of effects of potential disease treatments.

Cellular and subcellular distribution of monocarboxylate transporters in cultured brain cells and in the adult brain

Monocarboxylate transporters (MCTs) are involved in the uptake and release of lactate, pyruvate, and ketone bodies. Studies of their distribution at both the mRNA and protein levels have highlighted the specific expression of MCT1, MCT2, and more recently MCT4 in the central nervous system. MCT1 was found strongly expressed by cortical astrocytes both in vitro and in vivo. It was also found at high levels on blood vessels, ependymocytes, and glia limitans. A subset of neurons in vitro exhibited a weak but significant MCT1 expression. In contrast, it was determined that MCT2 represents the predominant neuronal MCT on cultured neurons as well as on neurons throughout the brain parenchyma. At the subcellular level, part of MCT2 is located in postsynaptic densities. Specific populations of astrocytes in the white matter also exhibited MCT2 expression in the rat, but not in the mouse brain. MCT4 was found exclusively in astrocytes in several areas including the cortex, the hippocampus, and the cerebellum. MCT2 expression increased in cultured neurons with days in vitro commensurate with increased synapse formation. Moreover, a significant increase in MCT2 expression was observed in cultured neurons exposed to noradrenaline, an effect involving a regulation at the translational level. The description of MCTs on different cell types in the central nervous system together with clear evidence for regulation of their expression further emphasize the important role that monocarboxylates, and particularly lactate, might play in brain energy metabolism not only during development but also in the adult.

Brain uptake and metabolism of ketone bodies in animal models

As a consequence of the high fat content of maternal milk, the brain metabolism of the suckling rat represents a model of naturally occurring ketosis. During the period of lactation, the rate of uptake and metabolism of the two ketone bodies, β-hydroxybutyrate and acetoacetate is high. The ketone bodies enter the brain via monocarboxylate transporters whose expression and activity is much higher in the brain of the suckling than the mature rat. β-Hydroxybutyrate and acetoacetate taken up by the brain are efficiently used as substrates for energy metabolism, and for amino acid and lipid biosynthesis, two pathways that are important for this period of active brain growth. Ketone bodies can represent about 30–70% of the total energy metabolism balance of the immature rat brain. The active metabolism of ketone bodies in the immature brain is related to the high activity of the enzymes of ketone body metabolism. Thus, the use of ketone bodies by the immature rodent brain serves to spare glucose for metabolic pathways that cannot be fulfilled by ketones such as the pentose phosphate pathway mainly. The latter pathway leads to the biosynthesis of ribose mandatory for DNA synthesis and NADPH which is not formed during ketone body metabolism and is a key cofactor in lipid biosynthesis. Finally, ketone bodies by serving mainly biosynthetic purposes spare glucose for the emergence of various functions such as audition, vision as well as more integrated and adapted behaviors whose appearance during brain maturation seems to critically relate upon active glucose supply and specific regional increased use.

犬肝流入血行遮断時の酢酸加リンゲル液の代謝効果

We compared the effects of infusions of Ringer's lactate (LR) and acetate (AR) solutions, on acid-base balance and hepatic energy metabolism during 40 min of hepatic inflow occlusion and 30 min of reperfusion in dogs. A slightly milder acidosis was observed in the group receiving AR, compared with the group receiving LR. After 40 min of occlusions in the LR group, ketone body concentrations in arterial and venous blood markedly decreased to a comparable level, indicating no uptake of ketone bodies in peripheral tissues. In contrast, in the group given AR, ketone body concentrations did not decrease during the inflow occlusion. Both the arterial concentration and arterio-venous concentration gradients were maintained, indicating sufficient supply and utilization of ketone bodies in the peripheral tissues. Moreover, the renal-venous concentration of ketone bodies was slightly higher than the arterial concentration, indicating renal ketogenesis during hepatic inflow occlusion in dogs receiving AR infusions. The hepatic energy levels (ATP+1/2ADP) in the AR group were significantly higher than in the LR group after 30 min of reperfusion. Due to the improved acid-base balance and sufficient ketone body supply to peripheral tissues, the metabolic burden of the liver after release of occlusion was considered to be smaller in the AR group. AR administration during hepatic ischemia is recommended.

Elevated venous glutamate levels in (pre)catabolic conditions result at least partly from a decreased glutamate transport activity.

Abnormally high postabsorptive venous plasma glutamate levels have been reported for several diseases that are associated with a loss of body cell mass including cancer, human/simian immunodeficiency virus infection, and amyotrophic lateral sclerosis. Studies on exchange rates in well-nourished cancer patients now show that high venous plasma glutamate levels may serve as a bona fide indicator for a decreased uptake of glutamate by the peripheral muscle tissue in the postabsorptive period and may be indicative for a precachectic state. High glutamate levels are also moderately correlated with a decreased uptake of glucose and ketone bodies. Relatively high venous glutamate levels have also been found in non-insulin-dependent diabetes mellitus and to some extent also in the cubital vein of normal elderly subjects, i.e., in conditions commonly associated with a decreased glucose tolerance and progressive loss of body cell mass.